1. Field of the Invention
This disclosure relates to polymer resins and, in particular, to polymer resins suitable for use in polymer interlayers, including those utilized in multiple layer panels.
2. Description of Related Art
Poly(vinyl butyral) (PVB) is often used in the manufacture of polymer sheets that can be used as interlayers in multiple layer panels, including, for example, light-transmitting laminates such as safety glass or polymeric laminates. PVB is also used in photovoltaic solar panels to encapsulate the panels which are used to generate and supply electricity for commercial and residential applications.
The term “safety glass” generally refers to a transparent laminate that includes at least one polymer sheet, or interlayer, disposed between two sheets of glass. Safety glass is often used as a transparent barrier in architectural and automotive applications, and one of its primary functions is to absorb energy resulting from impact or a blow without allowing the object to penetrate the glass. Additionally, even when the applied force is sufficient to break the glass, the polymeric interlayer helps keep the glass bonded to the laminate, which prevents dispersion of sharp glass shards, thereby minimizing injury and damage to people or objects within the interior space. Safety glass may also provide other benefits, such as a reduction in ultraviolet (UV) and/or infrared (IR) radiation, and it may also enhance the aesthetic appearance of window openings through addition of color, texture, and the like. Additionally, safety glass with desirable acoustic properties has also been produced, which results in quieter internal spaces.
Often, polymers that exhibit one set of desirable properties, such as acoustic performance, lack other desirable properties, such as impact resistance or strength. Therefore, in order to achieve certain combinations of properties, multilayered polymer interlayers have been used. These multilayered interlayers may include at least one inner “core” layer sandwiched between two outer “skin” layers. Often, the core layer of an interlayer may be a softer layer having a lower glass transition temperature, which enhances its acoustic performance. However, because such resin layers can be difficult to easily process and/or transport, the skin layers of such multilayered interlayers are often stiffer and have higher glass transition temperatures, which imparts enhanced processability, strength, and impact resistance to the interlayer. In some cases, the outer layers may be formed from the lower glass transition materials, with the inner core layer being the stiffer layer.
At times, use of various resins having different properties can also produce optical defects within the interlayer. For example, one defect common to these types of compositions, layers, and interlayers is mottle. Mottle is an objectionable form of optical distortion or visual defect appearing as uneven spots or texture, usually in the final structure. Mottle is caused by small-scale surface variations at the interfaces between the soft and stiff layers wherein the individual layers have different refractive indices. Clarity is another important optical property that is determined by measuring the level of haze within the composition, layer, or interlayer. High haze typically occurs when different types of optically incompatible polymers and/or plasticizers are blended or mixed together. In such mixtures, light passing through the blend is scattered as it encounters regions of different polymer materials, and the result is a hazy, visually unclear appearance. High clarity polymers and interlayers are those having very low haze values. Thus, a need exists for polymer resin compositions, resin layers, and interlayers formed from blends of poly(vinyl acetal) resins that have different compositions, but that exhibit desirable optical properties. Additionally, such compositions, layers, and interlayers should be produced without sacrificing mechanical and acoustic performance of the final product and should be usable in a wide variety of end use applications, including as automotive and architectural multiple layer panels.